The present invention generally relates to wireless communications nodes, and in particular to such devices which have the independent ability to form communications networks.
Ultra-wideband (UWB) radio is a method of RF/wireless communications utilizing short duration pulses instead of a continuous wave sinusoid to transmit information. Whereas continuous wave signal is constantly active both during data transmission as well as after, an UWB signal is only active during pulse transmissions, which allows the R.F. front end to be turned off during inactive periods.
It is well known that the time-limited, wide spectrum signaling in UWB promises greater network capacity over traditional radio architectures, allowing superior data-rate and spatial capacity at similar power consumption over short distances. The short pulse signaling also allows duty cycling of the RF front end to save power. However, achieving these benefits of ultra-wideband communications is contingent on precise synchronization between transmitter and receiver such that transmitted pulses are received. For instance, if a transmitter and receiver are not synchronized to the same clock and a pulse is transmitted, the receiver may not be active and miss the data. However, if the two are synchronized together, then the receiver will be able to capture the pulse even as the receive duty cycle is reduced.
A popular practical implementation of synchronization is in the use of a high speed DLL/PLL in conjunction with a digital pulse tracking backend that maintains synchronization throughout the period of communications. The drawback of this approach is that the receiver and transmitter clocks must have center frequencies matched on the order of ten to hundreds of parts per million to maintain adequate synchronization, thereby necessitating that the local oscillators of both the transmitter and receiver be referenced to well matched crystals so that frequency drift between them is minimized. This requirement for a crystal imposes a significant cost to a system that a manufacturer would ideally like to avoid.